Typical power converters are comprised of a switching circuit consisting of a plurality of switching elements connected in series, and a smoothing capacitor connected in parallel to the switching circuit. An example of such power converters is disclosed in a first patent document, and another example of them is disclosed as a motor control apparatus in a second patent document.
The power converter disclosed in the first patent document is comprised of a power converting circuit, a smoothing capacitor, and a controller. The power converting circuit is configured such that three legs each consisting of series-connected two switching elements are connected in parallel to each other. The power converting circuit and the smoothing capacitor are connected between the positive terminal and the negative terminal of a DC power source.
For power conversion, the controller turns on or off the switching elements of the power converting circuit at preset timings to convert DC power outputted from the DC power source into three-phase AC power, thus supplying the three-phase AC power to a motor.
On the other hand, for discharging the smoothing capacitor, the controller turns on the two switching elements of a leg simultaneously to discharge the charge stored in the smoothing capacitor. This prevents electrical shock due to the charge stored in the smoothing capacitor.
The motor control apparatus disclosed in the second patent document is provided with a converter, a low-side capacitor, a high-side capacitor, and an MG_ECU. The converter has two transistors connected in series. The low-side capacitor and the low-side transistor of the two series-connected transistors are connected between the positive and negative terminals of a battery. The two series-connected transistors and the high-side capacitor are connected between input terminals of an inverter.
For power conversion, the MG_ECU turns on or off the two transistors of the converter at preset timings to convert DC power with a low voltage outputted from the battery into DC power, thus supplying it to the inverter.
On the other hand, for discharging the high-side capacitor, the MG_ECU turns on the low-side transistor of the two transistors of the converter, and turns off the high-side transistor, thus discharging the charge stored in the low-side capacitor. Thereafter, the MG_ECU turns on the low-side transistor, and turns on the high-side transistor, thus discharging the charge stored in the high-side capacitor. This charges the low-side capacitor. Thereafter, these operations are repeated, so that the charge stored in the high-side capacitor is discharged. That is, alternately turning on the low-side transistor and the high-side transistor discharges the charge stored in the high-side capacitor. This prevents electrical shock due to the charge stored in the high-side capacitor.